1. Field of the Invention
The present invention relates to a lamp to be driven from a source of microwave energy and having an electrodeless plasma discharge.
In the Parent application Ser. No. 12/227,750, the plasma discharge is in a bulb in a ceramic receptacle. In this Continuation in Part, the bulb and the ceramic receptacle are replaced by a two-region/two-volume arrangement.
Efficient coupling of microwave energy into the bulb is crucial to strongly exciting the contents of the bulb, to cause it to incandesce. For this reason, air wave guides have not been successful for this purpose.
2. Description of the Related Art
In U.S. Pat. No. 6,737,809, in the name of F M Espiau et al., there is described:
A dielectric waveguide integrated plasma lamp with a body consisting essentially of at least one dielectric material having a dielectric constant greater than approximately 2, and having a shape and dimensions such that the body resonates in at least one resonant mode when microwave energy of an appropriate frequency is coupled into the body. A bulb positioned in a cavity within the body contains a gas-fill which when receiving energy from the resonating body forms a light-emitting plasma. (Despite reference to a “bulb”, this specification does not describe a discrete bulb, separable from the lamp body.)
In our European Patent No. EP2188829—Our '829 patent, there is described and claimed (as granted):
A light source to be powered by microwave energy, the source having:
                a body having a sealed void therein,                    a microwave-enclosing Faraday cage surrounding the body,                        the body within the Faraday cage being a resonant waveguide,        a fill in the void of material excitable by microwave energy to form a light emitting plasma therein, and        an antenna arranged within the body for transmitting plasma-inducing, microwave energy to the fill, the antenna having:                    a connection extending outside the body for coupling to a source of microwave energy;wherein:                        the body is a solid plasma crucible of material which is lucent for exit of light therefrom, and        the Faraday cage is at least partially light transmitting for light exit from the plasma crucible,the arrangement being such that light from a plasma in the void can pass through the plasma crucible and radiate from it via the cage.        
As used in Our '829 patent:
“lucent” means that the material, of the item which is described as lucent, is transparent or translucent—this meaning is also used in the present specification in respect of its invention;
“plasma crucible” means a closed body enclosing a plasma, the latter being in the void when the void's fill is excited by microwave energy from the antenna.
We describe the technology protected by Our '829 patent as our “LER” technology.
We have filed a series of patent applications on improvements in the LER technology.
There are certain alternatives to the LER technology, the principal one of which is known as the Clam Shell and is the subject of our International Patent Application No PCT/GB08/003,811. This describes and claims (as published):
A lamp comprising:
                a lucent waveguide of solid dielectric material having:                    a bulb cavity,            an antenna re-entrant and            an at least partially light transmitting Faraday cage and                        a bulb having a microwave excitable fill, the bulb being received in the bulb cavity.        
The LER patent, the Clam Shell application and the LER improvement applications have in common that they are in respect of:
A microwave plasma light source having:
                a of solid-dielectric, lucent material, having;                    a closed void containing electro-magnetic wave, normally microwave, excitable material; and                        a Faraday cage:                    delimiting a waveguide,            being at least partially lucent, and normally at least partially transparent, for light emission from it,            normally having a non-lucent closure and            enclosing the fabrication;                        provision for introducing plasma exciting electro-magnetic waves, normally microwaves, into the waveguide;the arrangement being such that on introduction of electro-magnetic waves, normally microwaves, of a determined frequency a plasma is established in the void and light is emitted via the Faraday cage.        
In this specification, we refer to such a light source as a Lucent Waveguide Electromagnetic Wave Plasma Light Source, with the express proviso that this term is not necessarily intended to infer that the fabrication of solid-dielectric, lucent material fills the Faraday cage. Having rejected LUWAG EMPLIS as an acronym we use the abbreviated acronym LUWPL to refer to the light source of the previous paragraph. We pronounce this “loople”.
For the purposes of this specification, we define “microwave” to mean the three order of magnitude range from around 300 MHz to around 300 GHz. We anticipate that the 300 MHz lower end of the microwave range is above that at which a LUWPL of the present invention could be designed to operate, i.e. operation below 300 MHz is envisaged. Nevertheless we anticipate based on our experience of reasonable dimensions that normal operation will be in the microwave range. We believe that it is unnecessary to specify a feasible operating range for the present invention.
In our existing LUWPLs, the fabrication can be of continuous solid-dielectric material between opposite sides of the Faraday cage (with the exception of the excitable-material, closed void) as in a lucent crucible of our LER technology. Alternatively it can be effectively continuous as in a bulb in a bulb cavity of the “lucent waveguide” of our Clam Shell. Alternatively again fabrications of as yet unpublished applications on improvements in our technology include insulating spaces distinct from the excitable-material, closed void.
Accordingly it should be noted that whereas terminology in this art prior to our LER technology includes reference to an electroplated ceramic block as a waveguide and indeed the lucent crucible of our LER technology has been referred to as a waveguide; in the this specification, we use “waveguide” to indicate jointly:                the enclosing Faraday cage, which forms the waveguide boundary,        the solid-dielectric lucent material fabrication within the cage,        other solid-dielectric material, if any, enclosed by the Faraday cage and        cavities, if any, enclosed by the Faraday cage and devoid of solid dielectric material,the solid-dielectric material, together the effect of the plasma and the Faraday cage, determining the manner of propagation of the waves inside the cage.        
Insofar as the lucent material may be of quartz and/or may contain glass, which materials have certain properties typical of solids and certain properties typical of liquids and as such are referred to as super-cooled liquids, super-cooled liquids are regarded as solids for the purposes of this specification.
Also for the avoidance of doubt “solid” is used in the context of the physical properties of the material concerned and not to infer that the component concerned is continuous as opposed to having voids therein.
There is a further clarification of terminology required. Historically a “Faraday cage” was an electrically conductive screen to protect occupants, animate or otherwise, from external electrical fields. With scientific advance, the term has come to mean a screen for blocking electromagnetic fields of a wide range of frequencies. A Faraday cage will not necessarily block electromagnetic radiation in the form of visible and invisible light. Insofar as a Faraday cage can screen an interior from external electromagnetic radiation, it can also retain electromagnetic radiation within itself. Its properties enabling it to do the one enable it to do the other. Whilst it is recognised that the term “Faraday cage” originates in respect of screening interiors, we have used the term in our earlier LUWPL patents and applications to refer to an electrical screen, in particular a lucent one, enclosing electromagnetic waves within a waveguide delimited by the cage. We continue with this use in this present specification.